1. Field of the Invention
The present invention relates to an image processing apparatus capable of subjecting image data to variable-length compression.
2. Description of the Related Art
In image processing apparatuses in which image data is subjected to variable-length compression and stored into, for example, a hard disk via a page memory, the system processing section generally performs, for example, a process for adding a fill bit to a code in units of blocks for compression (i.e., in units of [n×n] pixels) to make the data length of each block constant. This is to facilitate data editing in the page memory. Further, since in variable-length compression, the code length in each block varies in accordance with the contents of an image, the data length is often set to the longest one that is expected in one-page image data, to avoid code truncation. Alternatively, it is set to a value that guarantees only a small truncation which has little influence on image quality.
However, in many cases, the actual code length of an image read by a scanner is much shorter than a data length set in light of the longest code length. Accordingly, also when the compressed data stored in the hard disk via the page memory is transferred to the printer again via the page memory, each block will be made to have a constant length near the longest code length. This being so, a greater amount of data than actually needed is processed, thereby overloading the system. This inevitably reduces the processing speed of the entire image processing apparatus.
In light of the above, there is a need for an image processing apparatus capable of adjusting the data length of each block in accordance with an image before making the data length of each block constant, thereby reducing the data amount of each page and hence reducing the load on the system.